I want to bond vertical carbon plates on another carbon plate. Look at the image to see what i am talking about. I am seaching for a really strong glue which will bond the two plates together, and it will offer some strength too because of the “shape” of the glue. Look at the red part of the image. Think of it like a weld between 2 metal plates.
I have tested this with epoxy resin, thickened with thixotropy enhancer. The bond is good but it is also brittle so it breaks quite easily. It’s not the plate that breaks but the “glue” and this is a problem. I then tried adding some small carbon cuttings to the mix, the glue was quite stronger but the final product was a mess and not able to make a nice “weld”.
Could you recommend another “glue”? It needs to be thick so it will not drop and also it must be strong and not brittle. Thanks in advance!
Methyl-acrylate glues are great for structural bonding
double…
Any links? Are these glues thick enough and most importantly are they compatible with epoxy? Thanks!
Loctite, araldite, plexus, etc have them in their product ranges. Thick enough, glues almost everything. I use it to glue doors, roof, bodypanels, all carbon/epoxy.
take a look at scott bader crystic crestomer too, I used it to glue hulls and decks, and internal structures. Epoxy was to stiff and brittle, a loud bang while sailing was the joint cracking. Using the crestomer fixed this problem.
Hysol makes a few good epoxies…always part specific. Some are metal filled, some not. I’ve used 9394 and 9309NA.3 with good results. Obviously, make sure your bonding area is well preped.
You might also be able to ADD a layer of carbon along the fillet also…almost like wet-layup over the epoxy bead.
how are you loading it? Whats the main criteria in the design? Obviously by the sounds of things, you want some more flexibility in the joint line?
I actually design a racing car diffuser and the vertical plates i am talking about are its vertical strakes. Look at the attached image to understand.
The forces on these plates will be modest (as the air passes around them) but they will also have to dampen any vibrations without cracking the bond. So, yes, the bond should be somewhat flexible.
In that case:
Plexus MA420 or 422 or 425 (only the working time differs).
The somewhat flexible nature of this glue dampens any vibration.
When I need to bond panels I use the same resin I used to laminate them, mix some ground fiberglass or flox, with cabosil, and then use it as a paste. if I used an infusion resin, I also purchase the same resin in the unreduced form. For example… I use Hydrex 100LV (Low viscosity) to infuse. Then I use Hydrex Thixo for the paste. I think its called thixo?
Usually that is enough, but in some cases you want a less brittle solution. Methacrylates are great for that.
2 examples (both boats)
-The Olympic 49er was glued with thickened resin in Europe, but with Plexus in Australia. The Australian boats did not have problems in the deck-to-hull joints, the European boats had cracks after even moderate use.
-One of my customers used Hexcel Redux 810 glue for certain parts. These came apart in some occasions. With Plexus (MA425 or MA1025, which is the low-shrink, low odour version) the stuff stays where it is supposed to be.
I contacted Araldite and they suggested me not to use this type of joint (T-joint) because the joint area is very small.
They recommend to use a joint like the one of the image attached.
It will certainly be better but not so easy because the joint line of the vertical plates i will use are not straight but curved.
Do you think that i will have good results with T-joints even using MMA adhesives or i should make a joint as shown in the image?
The joint in the picture has more bonding area, and uses less glue. So it’s better anyway. however, you stated you don’t use the full strength of the glue, and this is a bit more work to produce probably, so why bother…
Whith a good surface prep, you probably will destroy the part before the glue fails anyway 
-The Olympic 49er was glued with thickened resin in Europe, but with Plexus in Australia. The Australian boats did not have problems in the deck-to-hull joints, the European boats had cracks after even moderate use.
yes, resin joints, especially thicker ones, are horrible in flexing constructions like deck-hull joints. I’ve used both in one type. Epoxy lost…
double again… I hate my router!
Here’s a handy website, based in the uk:
http://www.vikingtapes.co.uk/3M_Products/3M_Adhesives/3M_EPX_Adhesives/
you could look at the acrylic adhesives too, but epoxy would be my choice in your case. I would want an aerofoil surface as stiff as I could, particularly the vertical surface like that. In my limited understanding, i would assume that the main section connecting the wing and car body would be the main damping section. Just a thought anyway…
I actually use MA glues to stiffen up cars. Epoxy just can’t handle the flex. Making the car stiff enough to make epoxy glue possible, would be very hard, very very expensive, and very, very, very heavy!
Laminating with resin and fibre would create a good joint, epoxy on its own is just too brittle for may applications
Just use the T-joint, plenty of strength in your application.
When i used thickened epoxy as a glue, the glue has broken quite easily while the part was intact.
Do you think a MA glue will be stronger than the part with a T-joint?
You are right. I want the vertical strakes to be stiff, so the joint should not be very flexible. But these vertical strakes will take some loads fromt the high velocity air and also they will always vibrate because of the car motion, bumps etc.
So i could accept a bit of flexibility only if it ensures that the joint will be strong and not brittle.
Believe me, Plexus MA425 is what you want, unless you want to bond with epoxy, then apply tabbing, which is ugly and a lot of work.
Flexibility is “high” but that is compared to epoxy. It is much, much stiffer than caulks. Actually, we have a sort of chair bonded with this material. If sitting on it, it does not move at all.